Thin film Magnetic Recording Media (MRM), such as hard disks, are used to store large amounts of data and are typically composed of multiple layers, including a non-magnetic substrate having sequentially deposited on each side thereof an underlayer and at least one magnetic layer. A carbon overcoat is typically deposited over the magnetic recording layer to protect the recording layer from wear and environmental corrosion.
A thin layer of lubricant is applied over the protective carbon overcoat to improve the tribological performance of the hard disk drive, so as to improve the durability and reliability of a magnetic recording medium. To this aim, the liquid lubricant must adhere to the carbon overcoat such that the rotational velocity of the disk does not cause a significant amount of the lubricant to be lost from the disk surface.
(Per)fluoropolyethers (PFPEs) and derivatives thereof are currently used in the lubrication of MRM.
KASAI PH, Raman V. Perfluoropolyethers with dialkylamine end groups: ultrastable lubricant for magnetic disk application. Tribology Letters. February 2002, vol.12, no.2, p.117-122. disclose that perfluoropolyether molecular chains are prone to undergo the intramolecular disproportionation reaction, which is catalysed by Lewis acid and, in the head-disk environment, it occurs when the successive ether oxygen flanking a methylene unit (—CF2—) come into contact with Lewis acid sites that may exist on the metal oxide surface.
However, it was shown that addition of X1P, partially fluorinated hexaphenoxy cyclotriphosphazene, markedly increases the durability of the magnetic disk system. The efficacy of X1P was attributed to the strong nucleophilic (Lewis base) nature of the triphosphazene ring. Accordingly, the above authors synthetized perfluoropolyethers with dialkylamine end groups of formula:R2N—CH2—CF2—O—[CF2CF2O]m—[CF2O]n—CF2—CH2—NR2 wherein —NR2 was a group deriving from di-n-propylamine and morpholine. However, this article does not disclose perfluoropolyethers terminated with dialkylamine end groups wherein the alkyl chain is substituted with at least one hydroxyl group.
Hydroxy-terminated polymeric materials comprising a (per)fluoropolyether backbone have been disclosed for example in U.S. Pat. No. 3,810,874 (MINNESOTA MINING AND MANUFACTURING COMPANY) May 14, 1974 , which relates to polyfunctional poly(perfluoroalkylen-oxides) and their preparation. Among the others, Example 1 provides a pre-polymer of formula (IV), wherein the alkyl chain bearing the hydroxy group is linked to the PFPE backbone through an amide moiety:HOCH2CH2NHC(O)—CF2O—(CF2CF2O)m—(CF2O)n—CF2—C(O)NHCH2CH2OH.  (IV)
U.S. Pat. No. 6,468,947 (SEAGATE TECHNOLOGY LLC) discloses a lubricant composition comprising a first fluoropolyether and a decomposition inhibiting amount of a second fluoropolyether having at least one nitrogen containing group, in particular an amine or amide moiety. In particular, examples of the decomposition-inhibiting lubricants comprise a fluoropolyether chain substituted with one or two groups comprising an amide moiety and having the following formula:—C(O)NH—CH2CH(OH)CH2OH.
U.S. Pat. No. 7,510,999 (HITACHI GLOBAL STORAGE TECHNOLOGIES) discloses a lubricant composition comprising a first liquid lubricant and a second liquid lubricant, wherein the first liquid lubricant contains a cyclotriphosphazene ring attached to at least one perfluoropolyether having a single terminal hydroxyl group and the second liquid lubricant contains a perfluoropolyether having two end groups selected from hydroxyl, tertiary amine and combinations thereof.
The second liquid lubricant can have the following structure (IIb):R1RN—[CH2]r—[CF2O]s—[CF2CF2O]t—[CF2O]u—CF2—[CH2]v—NRR1  (IIb)wherein R and R1 are independently selected from —[OCH2CH2]yOH, —OCH2CH(OH)CH2OH, —CH2CH2OH and —CH2CH2CH3 and wherein y is an integer from 1 to 6.
In particular, suitable second liquid lubricants have the following chemical structures ZDEA and ZEEA:
ZDEA:[HOCH2CH2]2—N—CH2—CF2O—[CF2CF2O]t—[CF2O]u—CF2—CH2—N—[CH2CH2OH]2;ZEEA:

US 2006052262 (MATSUMURA OIL RESEARCH CORP.) discloses a compound of formula (I), a lubricant and a magnetic disk using the compound of formula (I):A-CH2CF2O(CF2CF2O)m(CF2O)nCF2CH2-B  (I)wherein A is amino group having hydroxyl group, B is hydroxyl group or amino group having or not having hydroxyl group, wherein m is a real number of 5 to 36 and n is a real number from 4 to 30.
US 2009/0318664 (SEAGATE TECHNOLOGY LLC.) discloses a compound comprising a backbone with a perfluoropolyether chain, one or more cyclophosphazene rings attached to or incorporated into the backbone.
WO 2014/195299 (SOLVAY SPECIALTY POLYMERS ITALY S.P.A.) discloses a method for manufacturing cyclophosphazenes PFPE derivatives to be used in lubrication of magnetic recording media (MRM), comprising the following steps:    1) 1) providing a mixture (M) containing:    a) a (per)fluoropolyether (PFPE) polyol [PFPE (Ppol)] comprising a fluoropolyoxyalkylene chain (Rf) having two chain ends, each chain end comprising at least one hydroxy group, and b) the corresponding alkoxide of perfluoropolyether (Ppol) [PFPE (Palk)], wherein the equivalent concentration of PFPE (Palk) in PFPE (Ppol) is lower than 30%, preferably ranging from 5% to 15%;    2) contacting mixture (M) with a perhalocyclophosphazene (CPhalo) to provide a mixture (M1) containing an equivalent ratio of PFPE (Palk)/(CPhalo) of at least 1;    3) allowing mixture (M1) to react until complete disappearance of P—Cl groups to provide a mixture (M2);    4) submitting mixture (M2) to hydrolysis to provide a mixture (M3);    5) optionally removing (Ppol) from mixture (M3) to provide a mixture (M4).
WO 03/067285 (CORNING INCORPORATED) discloses compounds having an aromatic or heteroaromatic moiety, at least two fluorinated alkylene, arylene or polyether moieties, each fluorinated alkylene, arylene or polyether moiety being linked to the aromatic or heteroaromatic moiety through an —O— or —S— linkage; at least one ethylenically unsaturated moiety, each ethylenically unsaturated moiety being linked to one of the fluorinated alkylene, arylene or polyether moieties.
US 2005/0277558 (HITACHI GLOBAL STORAGE TECHNOLOGIES NETHERLANDS B.V) discloses a lubricant composition for use as a lubricant for magnetic recording media, comprising a first liquid lubricant and a second liquid lubricant, wherein the first liquid lubricant contains a cyclotriphosphazene ring attached to at least one perfluoropolyether having a single terminal hydroxyl group, and the second liquid lubricant contains a perfluoropolyether having two end groups selected from hydroxyl, tertiary amine, and combinations thereof.